America's deadliest sniper was one of two people shot dead by a war veteran at a Texas gun range.

A friend says former Navy Seal and American Sniper author Chris Kyle and his friend Chad Littlefield, had taken their alleged killer to the range to try and help him as he suffered post-traumatic stress disorder.

Sergeant Lonny Haschel said in a news release that 25-year-old Eddie Ray Routh of Lancaster had been arraigned on two counts of capital murder. Routh was being held on a combined US$3 million (NZ$3.5m) bond.

Kyle was rated as the most deadly sniper in US history.

He had a confirmed 160 kills from a claimed 255 during the Iraq war and became so feared by insurgents they put a US$80,000 bounty on his head and nicknamed him al-Shaitan Ramad, or "the Devil of Ramadi", the Daily Mail reported.

His greatest achievement was reported top be his longest kill from 1.9 kilometres away.

Haschel said Erath County Sheriff's deputies responded to a call about a shooting at the Rough Creek Lodge, west of Glen Rose, at about 5.30pm Saturday (12.30am Sunday, NZT). Police found the bodies of Kyle, 38, and Littlefield, 35, at the shooting range about 80 kilometres southwest of Fort Worth.

Travis Cox, the director of a nonprofit group Kyle helped found, said Kyle and Littlefield had taken Routh to the range. Littlefield was Kyle's neighbour and "workout buddy".

"What I know is Chris and a gentleman took a veteran out shooting who was struggling with PTSD to try to assist him, try to help him, try to, you know, give him a helping hand, and he turned the gun on both of them, killing them," Cox said.

Police said Routh opened fire on Kyle and Littlefield and then fled in a Kyle's pickup truck. Routh later arrived at his home in Lancaster, about 30 kilometres southeast of Dallas. Police arrested him after a brief pursuit and took him to the Lancaster Police Department.

The motive for the shooting was unclear.

Kyle, a decorated veteran, wrote the best-selling book, American Sniper: The Autobiography of the Most Lethal Sniper in US Military History, detailing his kills of insurgents from 1999 to 2009.

Kyle said in his book that Iraqi insurgents had put a bounty on his head. He served four combat tours of duty in Iraq and elsewhere, and he won two Silver Stars and five Bronze Stars for bravery, according to his book.

Cox described Littlefield as a gentle, kind-hearted man who often called or emailed him with ideas for events or fundraisers to help veterans.

"It was just two great guys with Chad and Chris trying to help out a veteran in need and making time out of their day to help him. And to give him a hand. And unfortunately this thing happened," Cox said.

Craft International, Kyle's security training company, had scheduled a US$2,950-per-person civilian training event at Rough Creek Lodge called the "Rough Creek Shoot Out!" for March 1-3. The price included lodging, meals and shooting instruction. Kyle was due to teach the first class, called "precision rifle."